Field of the Disclosure
The present disclosure relates to a display device, and more particularly, to a holographic display. Although the present disclosure is suitable for a wide scope of applications, it is particularly suitable for implementing a holographic display with a stereoscopic display of colors by changing a structure and mitigating flickering by lowering a response speed.
Discussion of the Background
While a conventional two-dimensional image system provides planar images, a three-dimensional image system displays actual image information about an object for observers. In this sense, the three-dimensional image system may be considered as the ultimate image display technology.
As techniques for reproducing three-dimensional stereoscopic images, stereoscopy, holography and integral imaging are under development. Among these technologies, holography enables an observer to see the same stereoscopic image as a real object without wearing goggles in viewing the holographic image created using laser light. For this reason, holography is known as the most ideal technology that produces an excellent stereoscopic effect to observers without causing eye fatigue.
Holography requires a spatial light modulator. The spatial light modulator functions to adjust transmittance of light or output phase information about light. Stereoscopy is a technology to separate an image into an image for the left eye and an image for the right eye. This technology allows observers to recognize a three-dimensional image based on binocular disparity by providing different pieces of information to both eyes. In contrast, holography presents distances and depths using the effect of interference of light. In holography, when light is emitted from a light source such as laser, which has an interference property, information about an interference image is delivered to the spatial light modulator. Then, the spatial light modulator outputs a three-dimensional image by diffracting the delivered interference image information.
Meanwhile, for a holographic display, which utilizes coherent diffraction of light, the diffraction capability is determined by the pixel size of the spatial light modulator (SLM), and a viewing window which is viewable by a viewer is determined by the diffraction capability. That is, as the pixel size of the SLM decreases, the diffraction capability increases, and a higher diffraction capability provides a wider viewing window. However, the pixel size, which is related to resolution, has limitations regarding processes. Accordingly, the viewing window obtained with an actually realized pixel size is only the size of a pupil of the viewer.
In addition, when stereoscopic display of colors is performed using a holographic display, it is impossible to transmit rays of light in different colors at the same time because the diffraction angle varies among the wavelengths of the rays of the respective colors. Thus, images of different colors are supplied at different times. Moreover, for one color, the left eye and right eye cannot be covered by one viewing window, and thus an image to be supplied to the viewer is divided into an image for the left eye and an image for the right eye. Accordingly, for a typical holographic display, a high response speed greater than the multiplication of a response speed necessary for display and a value of hue necessary for colors to be realized is required, and thus issues such as afterimage effect and flickering are raised in implementing stereoscopic display of colors.